xyzulu I just tried this and it works too: systemctl mask postfix
It seems appcd was restarting the service.
Jul 2 17:09:40 enhance-panel appcd[793]: [2024-07-02T21:09:40Z ERROR appcd::mail_server_monitor] Unable to connect to postfix, restarting
Jul 2 17:09:40 enhance-panel appcd[719938]: Failed to restart postfix.service: Unit postfix.service is masked.